the king punch didn't leave a scratch

I get that is always used as the biggest feat of that barrier, but what feat has the King Punch really done in the series so far? It has the reputation "to be able to defeat a Yonko", but on how many Yonkos has that ever been tested on?

My guess would be, 0. The punch never has been landed on a Yonko to see if it actually would be enough to defeat a Yonko.

Unless we got something else in future, like him actually landing on a Yonko to see what happens, it is just an event that has never occured in the story. And I am quite sure he never defeated a Yonko with it yet because it surely would have been a crazy feat that would been mentioned by now already.